1. Field of the Invention
The invention relates to gas lasers and more specifically to a gas laser construction and method for obtaining a single line polarized operation in an internal mirror configuration.
2. Background Art
The advantage of one hundred percent (100%) single line operation in a gas laser such as an argon gas laser has been recognized but difficult to achieve.
It is known to use a half-Littrow prism in combination with a curved mirror to produce single line operation of a gas laser. This has been done by mounting both optical elements external of the laser tube and terminating the tube with windows placed at the Brewster angle. However, this system does not provide the several advantages of being able to use internal rather than external optics.
U.S. Pat. No. 4,746,201 refers to use of prism surfaces at the Brewster angle and schematically illustrates use of prisms within a gas laser tube but provides no specific indication of how the prisms would be mounted. Further, there is no indication of how the prisms could be replaced if contaminated after use.
With further regard to internal optics, it is known to attach optical mirrors to a gas laser tube to form an internal mirror tube as shown in U.S. Pat. No. 4,477,907. This provides what is commonly called a gas laser with integral mirrors. While not described as such, the optical mirrors referred to in the '907 patent were secured using a frit seal. However, frit seals are known to degrade when exposed to high temperature cycling and are difficult to remove if contaminated. As an improvement over frit sealed mirrors, mirrors have been attached with a cold weld to form a tube with integral mirrors. This construction is illustrated in U. S. Pat. No. 4,803,697. Various manufacturing considerations become involved when the cold weld method is employed.
In another form of internal optics for a gas laser, it is known to contact optical elements such as windows to form the tube terminations. This method as well as the cold weld method is advantageous because the elements may easily be removed during processing if they become contaminated. Thus, overall an internal optics system is to be preferred over an external optics system for a gas laser such as an argon gas laser.
With respect to achieving line purity, it is known to attach narrow band-width mirrors to reduce the number of lines produced by the laser so as to achieve ninety-five percent (95%) line purity. It has heretofore been considered virtually impossible to provide one hundred percent (100%) line purity with a mirror or window coating. The typical coating is known to be very sensitive to process variables such as temperature, pressure and the like. Thus, it would be desireable to achieve 100% line purity without total dependence on the coating employed.
It is also known to provide polarizing elements to achieve polarized light. Such an operation is achieved in a window tube by using windows at the Brewster angle and a polarized light operation is of course desireable in a gas laser.
With the foregoing in mind, there is thus a need to provide an improved gas laser construction having replaceable internal optics capable of producing one hundred percent (100%) line purity in the form of polarized light. The provision of such a laser and the method of achieving such operation thus become the principle objects of the present invention. Other objects will appear as the description proceeds.